Wing tip shape for a wing, in particular of aircraft

ABSTRACT

A wing for of aircraft has a wing tip shape that has a profile that extends in the direction of the span of the wing, and across the direction of the span of the wing extends from the wing leading edge to the wing trailing edge. The profile is delimited by a first skin and a second skin, with a winglet, arranged on the wing end. The winglet is substantially planar, and has a transition region arranged between the wing and the winglet, that extends from a connection on the wing to a connection on the winglet. The curvature of the local dihedral can increase in the transition region from a low level or a level of zero at or near the wing intersection in the outboard direction.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation, of U.S. patent applicationSer. No. 12/515,825, filed on May 21, 2009, which application is anational phase entry under 35 U.S.C. §371 of International ApplicationNo. PCT/EP2007/010096 filed Nov. 21, 2007, which claims priority fromGerman Patent Application No. 10 2006 055 090.0 filed Nov. 21, 2006 andof U.S. Provisional Patent Application No. 60/872,704 filed Dec. 4,2006, all of which are hereby incorporated herein by reference.

FIELD OF INVENTION

The invention relates to a wing tip shape for a wing, in particular ofaircraft.

BACKGROUND OF THE INVENTION

Wing tip shapes, in particular for wings of aircraft, have been knownfor a long time and have already been examined in detail. The design ofwing tip shapes is of essential importance in the development ofpresent-day commercial aircraft and transport aircraft, which areoperated at high transonic speeds (Mach 0.65 to Mach 0.95). The totaldrag of an aircraft wing operating in the transonic range is essentiallycomprised of wave drag, profile drag, induced drag and parasitic drag.The induced drag in turn essentially depends on the lift distribution onthe wing, and on the wingspan. Therefore a reduction in the induced dragis most easily obtained by an increase in the wingspan. However, due tostructural, industrial and operational constraints this is not possibleto an unlimited extent.

One option for reducing the induced drag at a constant wingspan consistsof the replacement of the planar tip shape of a wing with a non-planarshape.

A possible non-planar tip shape is a winglet, which is provided on thewing tip. Main geometrical parameters are the height, the taper ratioand the dihedral angle. The dihedral angle of the winglet can differsignificantly from the dihedral angle of the wing and is typicallyconstant or almost constant over the winglet span. If the dihedral angleof the winglet is constant or almost constant the winglet is denoted asplanar or almost planar.

Generally speaking it has been shown that vertical winglets with analmost perpendicular transition between the wing and the winglet providethe most effective option for reducing the induced drag. However, theregion of the transition from the wing to the winglet poses a problem,as in this region, due to interference effects in transonic flight,undesirable shock waves easily occur. The shock waves on the wing, whichare a common and fundamental aspect of transonic aircraft operation,have a negative effect on the region of transition from the wing to thewinglet, and in turn lead to an increase in the wave drag. Therefore,overall, the potential provided by vertical winglets cannot be fullyutilised.

From U.S. Pat. No. 5,348,253, a wing tip shape for a wing of an aircraftis known, on which wing a winglet, provided on the wing tip, whichwinglet is essentially planar, is arranged at a transition region whichextends from a connection on the wing to a connection on the winglet.The transition region, in which the local dihedral shape from the wingto the winglet makes a continuous transition, is in the shape of acircular arc with a radius of curvature that lies within narrow limits,which shape is determined by the height of the winglet, by saidwinglet's angle of inclination in relation to the wing span (cantangle), and by a constant parameter of curvature. This known wing tipshape is suitable for significantly reducing the induced drag; however,due to interference effects in the region of the circular-arc shapedtransition from the wing to the almost planar winglet there is atendency towards an undesired level of wave drag.

Furthermore, from DE 101 17 721 A1 or B4, corresponding to US2002/0162917 A1 or U.S. Pat. No. 6,722,615 B2, a wing tip extension foran aircraft wing is known, which wing tip extension between a connectionregion for connection with the wing and the tip of the wing tipextension provides a continuous increase in the local dihedral, combinedwith a continuous increase in the sweep of both the leading edge and thetrailing edge and a continuous decrease in the depth of the wing tipextension. As far as the angle of the local dihedral is concerned, it isstated that said angle is to increase from 0° to 10° in the connectionregion to the wing up to 45° to 60° at the tip of the wing tipextension. This known design of the wing tip extension results in a lowlevel of interference and consequently low level of wave drag. However,the height that can be attained with this wing tip shape is limited, andthere is little discretion in the selection of the design of the wingtip region if compared to the design of an added winglet.

Finally, from U.S. Pat. No. 6,484,968 B2 an aircraft is known withwinglets provided on the ends of the wing, wherein the winglets followan elliptical curve. The proposal of U.S. Pat. No. 6,484,968 B2 againdefines a connection in which the curvature of the wing tip shape in theconnection region to the wing is at its maximum and then along the wingspan decreases, which is exactly contrary to the requirements definedlater on, so that with this wing tip shape, too, undesired interferenceeffects lead to an increase in the wave drag.

BRIEF SUMMARY OF THE INVENTION

It is the object of the invention to provide a wing tip shape that onthe one hand to the fullest extent possible makes use of the advantageprovided by high winglets in relation to a reduction in the induceddrag, while on the other hand reducing interference effects in thetransition region from the wing to the winglet to a minimum.

This object is met by a wing tip shape with the features of claim 1.

Advantageous embodiments and improvements of the wing tip shapeaccording to the invention are provided in the dependent claims.

The invention provides a wing tip shape for a wing, in particular ofaircraft, which wing comprises a profile that extends in the directionof the span of the wing and across said direction of the span of thewing extends from the wing leading edge to the wing trailing edge, whichprofile is delimited by a first skin and a second skin, with a winglet,arranged on the wing end, which winglet is essentially planar, and witha transition region arranged between the wing and the winglet, whichtransition region extends from a connection on the wing to a connectionon the winglet, wherein in the transition region the local dihedral fromthe wing to the winglet makes a continuous transition. The inventionprovides for the curvature of the local dihedral in the transitionregion an increase from a low level or a level of zero near theconnection of the transition region to the wing up to a maximum near bythe connection of the winglet to the transition region in the outboarddirection.

This curvature characteristic may be present at at least one curveformed by constant chordwise points in the transition region along thespanwise dimension, which could be as an example the Leading Edge.Further examples are the trailing edge or a curve formed by points at50% chord. This depends on the requirements for the specific wing tipshape design to achieve a good surface quality. That is, in terms of thesurface formed by the transition region, at least part of the transitionregion, when viewed in cross-section, presents a curve which has anincreasing curvature of local dihedral in the outboard direction.

Investigations relating to the dependence of the interference effects onthe geometry and the boundary conditions of flow, on whichinvestigations the invention is based, have shown that the interferenceeffects described in the introduction, which interference effects occurin the region of the transition from the wing to the winglet in thetransonic region, significantly depend on the curvature along the wingspan. This dependence shows that the curvature in the region of a highprofile load, i.e. a large ratio of local lift to local profile depth,has to be as small as possible, and can also increase as the profileload decreases. In order to minimise the induced drag it is advantageousif less aerodynamic load has to be generated on the winglet than on thewing. For this reason a wing tip shape that is to attain a certainheight (above the wing) should start with the least possible curvature,which then can increase the steeper the wing tip shape becomes, and thefurther distant said wing tip shape is from the wing plane.

Using the example of an ellipse, it can be derived that the demand for asmall curvature in the connection region of the wing and subsequentlycontinuously increasing curvature constraints the height to be achievedwith such a defined wing tip shape. FIG. 4) illustrates this fact, wherea section of an ellipse, standardised to a maximum width of 1 forvarious ratios of large axis a to small axis b is shown, i.e. a/b=1(circle), a/b=1.2, and a/b=1.5. This justifies the demand for a largeplanar winglet (advantageously at least 50% of the total height of thewing tip shape) following a transitional arc arrived at taking intoaccount the findings obtained, so as to be able to ensure a highreduction in the induced drag.

To provide a smooth connection between the transition region and thewinglet it can be beneficial to have in this area a local reduction incurvature. As the benefits of the invention are maintained it ispossible to provide a transition region in which the curvature of thelocal dihedral increases from a low level or a level of zero near thewing connection over between 50% and 90% of the spanwise dimension ofthe transition region, up to a maximum.

Preferably, in the transition region the curvature of the local dihedralbegins to increase at the wing-side connection of the transition region.

It can be provided for the wing tip shape to extend at maximum over aregion of 5 to 20% of the semispan of the wing.

An advantageous embodiment of the invention provides for the wing tipshape to extend at maximum over a region of 10% of the semispan of thewing.

An advantageous embodiment of the invention provides for the planarwinglet to extend over at least 50% of the total height of the wing tipshape above the wing. Such dimensioning of the planar winglet, combinedwith a low curvature of the local dihedral in the connection region ofthe wing and then an increasing spanwise curvature of the local dihedralin the transition region according to the principles of the invention,ensures a large reduction in the induced drag in combination with smallinterference effects and low wave drag.

An advantageous embodiment of the invention provides for the planarwinglet to be inclined up to 45 degrees in relation to the vertical x-zplane.

The invention can provide for the planar winglet to be inclined up to 60degrees in relation to the vertical x-z-plane.

The invention can provide for the planar winglet to be inclined up to 80degrees in relation to the vertical x-z-plane.

The winglet inclination to the vertical plane may also be termed ‘cantangle’ as it is commonly known in the art.

There can be continuity of the tangent line of the local dihedral at theconnection between the wing and the transition region.

There can be continuity of the tangent line of the local dihedral at theconnection between the transition region and the winglet.

The leading edge of the transition region at the connection can make atransition, at a continuous tangent line, to the leading edge of thewing.

An advantageous embodiment of the invention provides for the sweep onthe leading edge of the wing tip shape to continuously increase up to apoint of largest sweep.

From the point of largest sweep, if this point is in the transitionregion, the leading edge of the transition region can make a transitionat a continuous tangent line to the leading edge of the essentiallyplanar winglet.

An advantageous embodiment of the invention provides for the point oflargest sweep on the leading edge to be at more than 75% of the spanwiselength, calculated from the connection on the wing to the connection onthe winglet, of the transition region.

According to an advantageous embodiment of the invention there iscontinuity of the tangent line of the leading edge over the entiretransition region.

BRIEF DESCRIPTION OF THE DRAWINGS

Below, an exemplary embodiment of the wing tip shape according to theinvention is explained with reference to the drawing.

The following are shown:

FIG. 1) a front view of a modern commercial aeroplane with a wing tipshape according to an exemplary embodiment of the invention;

FIG. 2) a lateral view of the commercial aeroplane shown in FIG. 1),with the wing tip shape according to the exemplary embodiment of theinvention;

FIG. 3a ) an enlarged front view of the wing tip shape according to theexemplary embodiment of the invention; and

FIG. 3b ) a top view of the wing tip shape of FIG. 3a ).

FIG. 4 illustrates relationship between a demand for a small curvaturein the connection region of the wing and subsequently increasingcurvature constraining the height achieved with such a defined wing tipshape.

DETAILED DESCRIPTION

FIGS. 1) and 2) show a commercial aeroplane on whose wing (1) a wing tipshape is provided that is formed by a winglet (3) and a transitionregion (2).

FIGS. 3a ) and 3 b) show in detail views of the exemplary embodiment,the wing (1) comprises a profile which is delimited by a first skin(11), the upper skin, and a second skin (12), the lower skin, and whichextends in the direction of the wing span and across it from a wingleading edge (8) to a wing trailing edge (7).

On the wing end the winglet (3) is provided, which is connected to thewing (1) by the transition region (2). The transition region (2) extendsfrom an imaginary or actual connection (4) on the wing (1) to animaginary or actual connection (5) on the winglet (3). In the transitionregion (2) the local dihedral, i.e. the angle in relation to the y-axisextending in the direction of the wing span from the wing (1) to thewinglet (3) makes a continuous transition. In the transition region (2),in other words from the connection position (4) on the wing side towardsthe connection position (5), the curvature increases from a low level ora level of zero in the outboard direction.

The spanwise dimension of the transition region is the linear dimensionof the transition region measured in the direction perpendicular to thelongitudinal axis of the aircraft.

The local dihedral from the wing (1) to the winglet (3) makes acontinuous transition, and in the transition region (2) the curvature ofthe local dihedral increases over at least substantially 50% of thespanwise dimension of the transition region up to a maximum and at most100% up to the winglet-side connection position (5). In the embodimentshown in FIG. 3a ) the curvature of the local dihedral begins toincrease at the wing-side connection (4) of the transition region (2)and increases over at least substantially 90% of the spanwise dimensionof the transition region (2) in the outboard direction up to a maximumlevel.

The transition region connects at the connection (4) to the wing (1),while the winglet (3) itself connects at the connection (5) to thetransition region (2). As has already been explained, the transitionregion (2) is characterised by an increase in the curvature of the localdihedral up to a maximum level.

The winglet (3) comprises a planar or almost or essentially planarshape, i.e. it has an essentially constant dihedral from the connectionposition (5) to its tip (13). Thus in the front view of FIG. 3a ) thewinglet (3) has an essentially constant inclination towards the y-axis.The geometric parameters of the winglet (3) can essentially be freelydefined so that it serves to optimally reduce the induced drag. On theother hand the transition region (2) is optimised to the effect thatinterference effects and thus the wave drag in this region are reducedto a minimum.

In the exemplary embodiment shown the wing tip shape extends at maximumover a region of 20% of the semispan of the wing (1), the planar winglet(3) extends over at least 50% of the overall height of the wing tipshape above the wing (1) and is inclined up to 45 degrees in relation tothe vertical x-z plane, i.e. the aircraft middle plane.

At the connection (4) between the wing (1) and the transition region(2), there can be continuity of the tangent line of the dihedral, i.e.at the connection (4) the tangent at the transition region (2) makes acontinuous transition to the tangent at the wing (1), with this beingadvantageous but not mandatory. Likewise, at the connection (5) betweenthe transition region (2) and the winglet (3) there can be continuity ofthe tangent line of the dihedral, with this being advantageous but alsonot mandatory. In the exemplary embodiment of the wing tip shapeaccording to the invention, which wing tip shape is shown in frontalview in FIG. 3a ), there is continuity of the tangent line of thedihedral shape in the y-z plane both at the wing-side connection (4) andat the winglet-side connection (5) of the transition region (2).

The top view, shown in FIG. 3b ), of the exemplary embodiment of thewing tip shape according to the invention in the x-y plane further showsa continuous-tangent-line connection of the leading edge (6) of thetransition region (2) to the leading edge (8) of the wing (1) on thesection point or connection point (4), which is again advantageous inhaving a beneficial effect on the airflow around the leading edge, butwhich is not mandatory. I.e. at the connection location (4) the tangentof the leading edge (6) of the transition region (2) can make acontinuous transition to the tangent of the leading edge (8) of the wing(1), which is again not mandatory.

The leading edge (6) of the transition (2) increases in curvature, thuscontinuously increasing the sweep up to a point (9) on the leading edge(6) of the transition region (2) or on the leading edge (10) of thewinglet (3). Advantageously, this point (9) of largest sweep is at over75% of the spanwise length, which is calculated from the wing-sideconnection location (4) (0%) to the winglet-side connection location (5)(100%), or on the leading edge (10) of winglet (3).

Starting at the point (9) of largest sweep, a continuous-tangent-linetransition from the leading edge (6) of the transition region (2) to theleading edge (10) of the almost planar winglet (3) is advantageous, ifpoint (9) is on the leading edge (6) of the transition region (2), butalso not mandatory.

In the exemplary embodiment shown, there is continuity of the tangentline of the leading edge (6) over the entire transition region (2),which provides a significant advantage but which is not mandatory.

The design of the trailing edge (7) of the transition region (2) canessentially be freely selected, provided the aerodynamic characteristicsof the wing tip shape are not negatively affected by it.

Although the invention herein has been described with reference toparticular embodiments, it is to be understood that these embodimentsare merely illustrative of the principles and applications of thepresent invention. It is therefore to be understood that numerousmodifications may be made to the illustrative embodiments and that otherarrangements may be devised without departing from the spirit and scopeof the present invention as defined by the appended claims.

LIST OF REFERENCE CHARACTERS

-   1 Wing-   2 Transition region-   3 Winglet-   4 Connection transition region to wing-   5 Connection winglet to transition region-   6 Leading edge of the transition region-   7 Trailing edge-   8 Leading edge of the wing-   9 Point of largest sweep-   10 Leading edge of the winglet-   11 Upper skin-   12 Lower skin-   13 Winglet tip

The invention claimed is:
 1. A wing tip device for a wing of anaircraft, wherein the wing tip device comprises: a substantially planarwinglet; a transition region connected to the substantially planarwinglet; wherein the wing tip device is configured to be mounted on anend of the wing, wherein the end of the wing comprises a profile that isdelimited by a first skin and a second skin, wherein the transitionregion extends from a first connection on the wing to a secondconnection on the substantially planar winglet, wherein geometricparameters of the substantially planar winglet are configured to reduceinduced drag, and wherein the transition region has a non-constantcurvature distribution of the local dihedral to reduce interferenceeffects.
 2. The wing tip device of claim 1, wherein in the transitionregion the radius of curvature of the local dihedral decreases over atleast substantially 50% of a spanwise dimension of the transition regionin the outboard direction up to a maximum.
 3. The wing tip device ofclaim 1, wherein in the transition region the radius of curvature of thelocal dihedral decreases over at least substantially 75% of a spanwisedimension of the transition region in the outboard direction up to amaximum.
 4. The wing tip device of claim 1, wherein in the transitionregion the radius of curvature of the local dihedral decreases over atleast substantially 90% of a spanwise dimension of the transition regionin the outboard direction up to a maximum.
 5. The wing tip device ofclaim 2, wherein in the transition region the radius of curvature of thelocal dihedral begins to decrease at the first connection of thetransition region.
 6. The wing tip device of claim 1, wherein the wingtip shape extends at maximum over a region of 5 to 20% of a semispan ofthe wing.
 7. The wing tip device of claim 1, wherein the wing tipextends at maximum over a region of 10% of a semispan of the wing. 8.The wing tip device of claim 1, wherein the substantially planar wingletextends over at least 50% of the total height of the wing above thewing.
 9. The wing tip device of claim 1, wherein the substantiallyplanar winglet has a cant angle of up to 45 degrees.
 10. The wing tipdevice of claim 1, wherein the substantially planar winglet has a cantangle of up to 60 degrees.
 11. The wing tip device of claim 1, whereinthe substantially planar winglet has a cant angle of up to 80 degrees.12. The wing tip device of claim 1, wherein the tangent line of thelocal dihedral is continuous at the first connection of the transitionregion.
 13. The wing tip device of claim 1, wherein the tangent line ofthe local dihedral is continuous at the second connection of thetransition region.
 14. The wing tip device of claim 1, wherein, at thefirst connection, a leading edge of the transition region transits at acontinuous tangent line to a leading edge of the wing.
 15. The wing tipdevice of claim 1, wherein at least one of the sweep on the leading edgeof the transition region and a sweep on a leading edge of thesubstantially planar winglet continuously increases in the outboarddirection up to a point of largest sweep.
 16. The wing tip device ofclaim 15, wherein the leading edge of the transition region transits ata continuous tangent line from the point of largest sweep to a leadingedge of the substantially planar winglet.
 17. The wing tip device ofclaim 15, wherein the point of largest sweep on the leading edge of thetransition region is at more than 75% of the unrolled length of thetransition region, calculated from the first connection to the secondconnection.
 18. The wing tip device of claim 1, wherein a tangent lineof the leading edge is continous over the entire transition region.